Exciton-Polaritons in Uniaxially Aligned Organic Microcavities

TL;DR

This paper reports the fabrication and optical analysis of uniaxially aligned organic microcavities with liquid-crystalline conjugated polymers, achieving record-breaking Rabi splitting energies and polarization-dependent coupling, advancing the field of organic polaritonics.

Contribution

It introduces a method to align organic microcavities with liquid-crystalline polymers, enabling unprecedented ultrastrong coupling energies and polarization control in organic microcavities.

Findings

Achieved Rabi splitting up to 1.80 eV in aligned microcavities.

Demonstrated polarization-dependent coupling strength.

First to reach visible spectrum Rabi splitting in organic microcavities.

Abstract

Here we report the fabrication and optical characterization of organic microcavities containing liquid-crystalline conjugated polymers (LCCPs): poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), poly(9,9-dioctylfluorene) (PFO) and poly(2,7-(9,9-dihexylfluorene)-co-bithiophene) (F6T2) aligned on top of a thin transparent Sulfuric Dye 1 (SD1) photoalignment layer. We extract the optical constants of the aligned films using variable angle spectroscopic ellipsometry and fabricate metallic microcavities in which the ultrastrong coupling regime is manifest both for the aligned and non-aligned LCCPs. Transition dipole moment alignment enables a systematic increase in the interaction strength, with unprecedented solid-state Rabi splitting energies up to 1.80 eV for F6T2, the first to reach the visible spectrum; with an optical gap of 2.79 eV this also gives the highest-to-date organic microcavity coupling ratio, 65$\%$. We also demonstrate that the coupling strength is polarization-dependent with bright polaritons photoluminescence for TE polarization parallel to the transition dipoles and either no emission or weakly coupled emission from the corresponding TM polarization. The use of uniaxally aligned organic microcavities with switchable coupling strength offers exciting prospects for direct observations of ultrastrong coupling signatures, quantum simulation, polaritonics and condensation related phenomena.